Objective  The mechanization level of seedling planting in China is relatively low. The seedling supporting mechanism is one of the key institutions in the seedling planting system of the seedling transplanter. The rack and pinion seedling supporting mechanism for the poplar seedling transplanter in China is developed to ensure the planting effect of the seedling transplanting equipment.

  Method  Firstly, aiming at the transplanting operation of long rod seedlings, the physical characteristics of fast-growing poplar seedlings were analyzed, the variation range data of seedling length and ground diameter were obtained, a design scheme of rack and pinion seedling supporting mechanism was proposed, the relationship between planting performance and motion parameters of rack and pinion seedling supporting mechanism was analyzed, the initial position of seedling supporting frame was calculated, and the working stroke of seedling supporting was determined. The contact collision algorithm was used to calculate the meshing constraints and motion parameters of gear and rack. We used ADAMS simulation software to establish and simulate the multi stiffness contact dynamic model of the seedling supporting mechanism, explore the influence of the gear rack modulus on the seedling supporting effect, analyze the accuracy of the seedling supporting movement through the displacement and speed change curve of the mass center of the seedling supporting frame, and verify the transmission performance of the seedling supporting mechanism structure through the change of transmission gear speed and the change of gear rack meshing force.

  Result  The module of gear and rack was 9, and the seedling raising effect was the best. At this time, the speed fluctuation of the center of mass of the seedling raising support frame in the forward direction was small, and the displacement change was stable. The displacement and time were approximately linear. The seedling raising process was close to uniform motion, and the speed was about 122 mm/s. The single working stroke of seedling supporting movement reached 599.9 mm, which met the design requirements of more than 568.4 mm. The power transmission of gears at all levels of seedling supporting mechanism was stable, the maximum contact force of tooth surface was 512.6 N, which was far less than the material strength, and there was no jumping and blocking.

  Conclusion  The simulation results show that the rack and pinion seedling supporting mechanism can meet the seedling supporting motion requirements of poplar seedling planting, realize zero speed transplanting, ensure the verticality of seedling planting, and effectively improve the previous seedling supporting methods in the process of seedling planting. It has good motion stability, safety and efficiency, and has a certain guiding role for afforestation machinery and equipment.